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What is a firewall?

CMS Vocational Training Hadyn Luke posted this on Thursday 9th of July 2020 Hadyn Luke 09/07/2020


What is a firewall?

You don’t need to be an IT specialist to have heard of firewalls – and you probably know that they are used to protect the information on your computer.

In this blog we look in more detail at what a firewall does, how your data might come under attack, and the different types of firewalls on the market.

What is a firewall?

A firewall is a defence mechanism that protects a home computer or network of computers from external threats. Firewalls are an essential tool for keeping your network secure and are often used in tandem with antivirus applications.

Threats can come from everyday activity such as visiting a website or clicking on an email link, and can expose your device to malware.

What is malware?

Malware is malicious software that can take different forms, such as:

  • A computer virus that infects, corrupts or deletes files
  • Spyware, which can follow your online activity and copy passwords or bank details
  • Ransomware, where your computer files are blocked and threatened with deletion unless you pay a ransom
  • Worms, which can enter through one computer and infect the whole network
  • Botnets, where malware is installed on your computer without your permission and becomes part of a network of compromised computers used for data theft, spam, leaks and other illegal activity

How are firewalls installed?

A firewall will be installed on a device or network either as software that can be added or as firmware that is already built in to the hardware of your computer, tablet or phone.

How does a firewall work?

Firewalls inspect data ‘packets’ – for example an email sent out or a news story read online – that enter or leave a network, and use a pre-determined set of rules to analyse whether they are safe or whether they might threaten the computer/network. They will then block these threats from affecting the system.

On a home computer the firewall is likely to be a fairly simple product, but corporate organisations usually have more complex needs, especially if for companies working over several interconnected sites.

What types of firewalls are there?

There are two main types of firewall: those that are known by how they filter data and those that are categorised by the system that they protect. Types of firewalls include:

  • Packet filtering firewall
  • Stateful inspection firewall
  • Circuit-level gateway
  • Application-level gateway
  • Next generation firewall

What else do firewalls do?

As well as protecting data, firewalls log any threats to the network, providing essential information that can be used to audit the system, identify new threats and work out ways to deal with them.

Advanced analysis of security helps to keep the network up and running, while allowing staff continual access to applications based in the cloud.

Why are firewalls so important?

The advance of technology, ever-changing threats from external bots and hackers, and the expansion of businesses over many sites can all cause concerns about network security.

While companies based in one building might stick with a LAN (Local Area Network), larger organisations will use a WAN (Wide Area Network) to connect several LANs together, and therefore need a more advanced suite of firewall products.

Many companies now offer more sophisticated product ranges that not only have advanced protection against malware, but also include application profiling, anti-spam options and web filtering. Some use DNS Sinkholing – which stops network users accessing malicious domains by giving a false IP address to specific URLs that threaten a network – as an extra level of protection.


If your organisation’s network has expanded, especially if it links head office computers with others on different sites or at employees’ homes, it’s especially important to regularly update your firewall provision. A system that might have covered you adequately a few years’ ago could be exposing your network to risk as your company grows and the sophistication of hackers increases. 

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